LED lighting systems are the lighting design of choice in many modern settings, notably in train and airplane cabins, due to high efficiency, low power consumption, long endurance and other advantages of LEDs. There are challenges in design and implementation of such electrical systems especially in environments where space is tight and access is limited or power needs to be transmitted to the LED's are over long distances. More specific to this disclosure, multiple voltage ranges may be used as the power input to the system that is normally handled by additional hardware.
At the Integrated Circuit (IC) level, LEDs are current driven devices where the light intensity is highly correlated with the current that is supplied to an LED.
LEDs have a very quick response time (˜20 nanoseconds) and instantaneously reach full light output. Rectifying the AC to DC conversion causes ripples in the voltage and current output from the driver to the LED. This ripple typically occurs at twice the frequency of the incoming line voltage. The LED output then correlates with the output waveform of the driver. Hence, there is needed a means to filter out these frequency noises and ripples which may cause undesirable intensity changes or flickers in the LED.
The relationship between the LED forward current and Relative Luminous Intensity of the LED STW8Q14D-EMC is relatively linear and close to 1:1. Thus constant light intensity may be achieved by maintaining constant forward current through the LED. Therefore, it is important to maintain a constant driving current. At present, several constant current IC designs exist, however the existing ICs that can function when more than 100V DC is applied have a topology that makes their output current dependent upon the input voltage. Consequently, variation in the input voltage would result in variations in output current and hence intensity fluctuations in the LED lights. For example, a typical IC data sheet reads (DIODES® Incorporated Data Sheet AL9910_A):
                    L        =                                                            (                                                      V                                          I                      ⁢                                                                                          ⁢                      N                                                        -                                      V                    LED                                                  )                            ×              D                                                      (                                  0.3                  ×                                      I                    LED                                                  )                            ×                              f                OSC                                              ⁢                                          ⁢          and                                    Eq        .                                  ⁢        1                                          t          OSC                =                                                            R                OSC                            +              22                        25                    ⁢          μs                                    Eq        .                                  ⁢        2            wherein L=Inductance, VIN=Input Voltage, VLED=Total voltage drop across the LED string, ILED=LED drive current, fosc=Switching frequency, Tosc=Oscillator period, Rosc=Switching frequency set resistor (in KΩ). See for example IC AL9910_1 data sheet link: www.diodes.com/assets/Datasheets/AL9910_A.pdf; LED STW8Q14D-EMC data sheet link: www.seoulsemicon.com/upload2/Specification_5630D_STW8Q14D_E3_Rev0.1_171220.pdf; Transistor DXT13003DG-13 from Diodes Incorporated data sheet www.diodes.com/assets/Datasheets/DXT13003DG.pdf; MOSFETS TN3N40K3 from STMicroelectronics data sheet link: www.st.com/content/ccc/resource/technical/document/datasheet/e1/9f/5b/ab/3e/c6/4b/21/CD00278221.pdf/files/CD00278221.pdf/jcr:content/translations/en.CD00278221.pdf. Based on Eq. 1, for instance a minimum variance of 26% in intensity fluctuation may result in from a range of 24V DC to 120V AC of the input power. To address this problem, the primary power needs to be pre-conditioned to accept the wide range of voltages. Additional power conditioning may electrically be inefficient.
Currently, multiple fixture types (e.g. one for 120V AC input and another for 24V DC input) are used to accommodate the multiple voltages received from multiple entry points. This solution requires more wiring, additional cavity of space to pass wires, and additional cost of parts and installations. These solutions are labor intensive and expensive. Maintenance and replacement of parts, inventory management, and schematic layouts are more complex with multiple fixtures. There exist designs that address a continuous power distribution from either an AC or a DC power supply but not from a single entry point for power. Some prior art use a linear topology for driving the LEDs via resistive/passive/linear methods. Over wide voltage ranges these methods are not power efficient. As an example, for the aforementioned voltage range of 24 VDC-120 VDC, the maximum efficiency of the driver at 120 VDC would be 20% for such systems. For main lighting in a rail environment, typically 6 W of LED power per foot is required to meet current lighting level specifications. In such a design with 20% efficiency, the LED lights could consume up to 30 W per foot that would result in consumption of 2400 W power over an 80 foot train.
Therefore, it would be advantageous to have a single fixture that allows a universal single electric power entry point for both AC and DC power and to provide a means to distribute power and signals to current loads, such as LED lighting systems, efficiently and reliably, along a long distance, and in particular, for distances greater than about 9m, and preferably greater than about 25m.